The present invention relates to a method of producing protective helmets, particularly for operators of motorcycles, in which the protective helmet is formed with the aid of a positive-type mold, on which successive layers of synthetic resin and fibrous tissue are formed.
In a known method of this type there is used a negative-type mold as a foundation. In a first operating step there are applied, for example by spraying, separating means and a cover-layer of resin to the interior of the negative-type mold, which contain the basic color and simultaneously form an outermost thin layer, of the helmet to be produced. Thereafter small strips of precut glass-fiber mats, impregnated with highly viscous polyester resin and hardening means, are applied to the still moist covering layer. Up to a maximum number of nine layers of polyester-type glass fibers are manually applied to the negative-type mold, and pressed into the mold by means of special tools, so as to be free of any bubbles. The relatively large number of the individual fibrous layers, as well as the consequently resulting high degree of resin remaining in the helment to be produced, inclusive of its outermost layer, and required both from a point of view of safety, as well as for manufacturing reasons, result in a relatively large weight of the helmet. This weight is further increased by any additional protective means required, such as an interior padding, acting as a shock absorber. Although the maximum weight for a complete protective helmet and accessories, but without a visor, is ordinarily determined by applicable test regulations, it is a helmet which has the least possible weight for a given high degree of protective quality which frequently influences a purchasing decision favorably.
In addition to the fiber-glass helmets mostly manufactured manually, there are also known helmets made of polycarbonate, produced exclusively by machine, which, as a rule, are lighter than the aforedescribed fiber-reinforced protective helmets. Although polycarbonate is a costly thermo-plastic material, which is difficult to process, helmets manufactured from polycarbonate, due to their being machine-produced, have a certain price advantage with respect to fiber-reinforced helmets. Even though the fabrication of fiber-reinforced helmets requires fewer investments in the form of machines or presses, than those needed for machine-produced helmets, such fabrication is, nevertheless, very labor-intensive, and consequently dependent on prevailing wage rates. The price- and weight-advantage of the polycarbonate helmet must be balanced against the vulnerability of its surface, to, for example, organic solvents or lacquers, and its relatively poor shock-absorbing capability; last but not least, the purchasing decision is often tipped in favor of the generally more costly and heavier fiberglass helmet for emotional reasons.